1. Technical Field
The invention relates to a mass spectrometer for analyzing isotopic signatures, with at least one magnetic analyzer and optionally with an electric analyzer as well, with a first arrangement of ion detectors and/or ion passages and, arranged downstream thereof in the direction of the ion beam, a second arrangement of ion detectors, with at least one deflector in the region of the two arrangements of ion detectors or between these arrangements. Additionally, the invention relates to a method for analyzing isotopes in a sample.
2. Prior Art
Preferred fields of application of the invention are geochronology and the control and regulation of nuclear processes.
The drive behind the invention is the desire for a measurement system that is as universal as possible.
Different elements, each with a plurality of isotopes, are of interest, particularly in the various methods found in geochronology.
By way of example, determining age using the mineral zircon is of importance, using both the so-called “uranium-lead method” and the “lutetium-hafnium method”. The details of these methods are of secondary importance to the invention. What is essential is that—this is usual in the case of a large background of the main constituents in the initial stone (the isotopes relevant to the uranium-lead method at best constitute a few percent, typically even only a few ppm, of the overall material)—the ratios of a plurality of isotopes have to be measured, e.g. 204Pb, 206Pb, 207Pb, 235U, 238U, and optionally further masses/isotopes in order to be sure of and correct the results. The same stone can also be dated using the Lu/Hf method, with the components being significantly more abundant in this case; in zircons HfO2 constitutes up to 30% (5% is typical), ThO2 up to 12%, U3O8 up to 1.5%.
The in part very different intensities must be measured using different detector types: Faraday collectors for high ion flows, Channeltron and secondary electron multipliers (SEM) for low and very low ones. Moreover, it may be necessary to introduce an energy barrier in order to remove the background of adjacent mass numbers (page 9 of the Triton/Neptune brochure by the applicant).
A further application is the measurement of (enriched) uranium, where mass numbers of 233, 234, 235, 236 and 238 are observed. Here 238U is the dominant isotope. In natural uranium, the isotope 235 is present in an abundance of approximately 0.7% and the isotope 234 is present in an abundance of approximately 5 ppm.
The measurements are typically carried out using (double focusing) multi-collector mass spectrometers in which different measurement channels are associated with the different isotopes. The type of measurement channel in this case depends on the (expected) intensity and the intensity of the neighboring channels.
In order to be able to carry out different types of measurements, multi-collector systems can either have moveable collectors (TFS Neptune or TFS Triton) or the mass-dependent spacing between the isotopes can be compensated for by an ion-optical element.
In a typical (prior art) design, moveable elements carrying Faraday and/or Channeltron detectors are kept available for universal use, as is a special channel with an ion counter (secondary electron multiplier) and a Faraday detector, with switching being possible between counting and Faraday operation. In this channel, there additionally is an energy barrier (RPQ) available in front of the counting detector.
Additionally, separate counting detectors (Channeltrons) can optionally be kept available, e.g. for measuring uranium, in particular for relatively high masses, where very small distances are required between the detectors for adjacent mass numbers.
Thermal ionization or inductively coupled plasma (ICP) can serve for ionization, e.g. after a preceding laser ablation of a sample.